Gotta get new headphones. I've always used IEMs but they've never lasted
more than a few months, so I'm considering getting full sized circumaurals
next. Looking into Superlux HD668Bs, Sony MDR-V6s and Audio-Technica
ATH M50s. Anyway, for those who've used them what are the pros and
cons and how do they compare to IEMs?

I've been told IEMs have "accurate quality" as opposed to a big live sound and
atmosphere. Always preferred that insular sound. Also heard that the sound quality
of circumaurals is better than that of IEMs of the same price, although that opinion
doesn't seem as clear cut.

I use AKG K702 headphones when mixing or listening late at night so as to not disturb the peace (give me loudspeakers any day). For on the go I use Sony MDR-Q68s. I don't like in ear listening apparatuses, I find them rather truncated in the extreme top end and inhibiting from a pure enjoyment perspective, plus I like being able to have better aural perception and awareness of my surroundings wherever I may be.

A lot of people will recommend the ATH-M50s, they are a well priced, good quality piece of gear. I myself would happily recommend them. I can't really comment on the Superlux cans; they appear to be a bit hit and miss for many and I've never been too fond of Sony's semi-pro gear either.

I have Klipsch S4's IEM's for on the go, and KRK KNS 8400's for at home. The Klipsch's definitely give way more isolation, full sized headphones will never beat IEM's are isolation. The S4's also sound great, even better with memory foam eartips. But I prefer headphones when at home(bigger sound, better soundscape, more comfy for long listening periods, etc). The 8400's are meant as monitoring headphones, so they are fairly flat, I got them to play guitar with when I can't be loud. And they rule for that, they also sound great for listening though. But since they are flat(ish) they will give you a more true sound whereas the S4's are meant just for listening, so they color the sound quite a bit.

If you want something portable S4's are wonderful. Honestly the S4's($80-ish) sound just as good as the 8400's($150). Depends if you want portability or not really.

I think with all said and done, it doesn't really matter. I've found flaws with nearly every pair of cans I've ever used. Chances are you'll be happy with your purchase, but unless you have some remarkable acces to all three pairs to try, your going off second hand information, which doesn't hold much weight for such a purchase. So all you can do is trust your ears, and your research skills. Regardless, you'll always wind up saying "I wonder if I would have liked that pair better/I wonder if I should have bought the cheaper ones instead".

I have Klipsch Image S4's (IEM) and Klipsch Image One (circumaural). They both sound fairly accurate (after 50 hours of burn-in). The Image One's do have better soundstage, although that's to be expected. But the comfort of my S4's is just unmatched.

Anything that sits on my head loses by a stretch to the S4's, which I forget wearing them.

Another advantage for IEM is that you can wear them in the rain. And if you plan to use your headphones on the go, circumaurals will drain your battery faster. Plus if the impedance of the headphones is too high, you'll need an amp to get the most out of them. (my Image One's are 32 ohm and perfectly driveable with most PMP's)

yeah but pink noise is so efficient, its just like white noise, but its even and balanced across all frequencies. What I do when I any new headphones is I just listen to music during the day and put it on pink noise while I sleep

fishbowl, I'm going to go against the grain here. The problem with 'break-in' (burn-in is a unrelated issue relating to electrical components) is that it's extremely difficult to test its validity. No real experiments have been conducted to indicate its existence.

What is real, however, is that any electromechanical device will alter its physical characteristics as a function of time; kind of obvious I know. But, the proponents of break-in forget that this idea that if you buy a pair of shoes and over some indefinite amount of time they begin to feel better is not strictly transferable to the experience of sound, or in fact how all headphones will respond due to the materials they use. A shoe conforming to the physical characteristics of a foot is a perfectly reasonable claim; headphones doing so on the other hand is not, in fact it's kind of ridiculous.

If you asked the average user of speakers or headphones, they would understandably tell you close to nothing about how they are manufactured or the treatments in which the materials use endure in order to attain certain responses at specific frequencies, or how those materials respond over time. The makers will endeavour to produce items that respond to frequencies in the way that they deem acceptable, and beneficial towards the tone they strive for, e.g. flat, bassy, etc. So, the tested response graphs you see manufacturers brandishing across their brochures are those measured with new headphones, and those which they deem adequate for the product's purpose. It should be unsurprising that over time, this response should change due to some elements of the design loosing their elasticity, but whether or not that make it "sound better" yields some bold claims, all of which are irregular and lack scientific evidence.

So, if you're thinking that running hordes of pink noise through your setup is going to make a shred of difference to your enjoyment, just remember: humans are terrible at remembering sound as it is heard, in that sonic acclimatisation is far more real an experience than break-in is. Humans suffer from the concept of confirmation bias, which means they will agree on certain parts of anecdotal assurances if it benefits their own perceptions of the world, which is why whenever someone tells me that my speakers will sound terrible if I don't perform some procedure on them, I'll usually eat a massive grain of salt to compensate.

It could be my brain, but with my last three sets of headphones (all Klipsch) I could always tell the
sound had improved after 50ish hours, without even expecting it with two models. The improvement I
would measure aroudn 30% tighter and clearer.